Turbocharger with sliding blades having combined dynamic surfaces and heat screen and uncoupled axial actuating device

ABSTRACT

A turbocharger having a variable geometry turbine intake incorporating a mobile cylindrical piston ( 70 ) for varying the area of the induction nozzle in the turbine ( 18 ). Blades ( 90 ) mounted on the piston for controlling the flow in the nozzle penetrate through a slotted heat shield ( 92 ) having a central opening wherein the rear disc of the turbine wheel is embedded to provide a smooth aerodynamic flow in the turbine vanes. A shield ( 100 ) engaged between the heat screen and a central housing of the turbocharger prevents the gas from the rear disc cavity from recycling into the cavity housing the blades further enhancing the aerodynamic flow. An axial actuating device ( 77 ) is secured for operating the piston via a shaft coupled by a cross ( 72 ) to the piston and coupled to an actuating hub ( 118 ) in the actuating device by quick connect unthreaded connection ( 122 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to turbochargers with variablegeometry. More particularly a turbocharger is provided having a turbineintake with a variable nozzle with sliding blades, with the bladesentering via a heat screen of slotted sheet metal suspended in thehousing of the turbine and having the turbine wheel embedded therein inorder to provide an aerodynamic surface directing the flow of exhaustgas in a turbine wheel with a substantially complete rear disc, anaerodynamic shield and an uncoupled axial actuating device to facilitatemounting.

2. Description of the Related Art

High-output turbochargers use variable-geometry systems for the turbinenozzle intakes in order to increase the performance and aerodynamicyield. Variable-geometry systems for turbochargers have typically beenof two types: a type with rotating blades and a type with a piston. Therotating blade type exemplified in U.S. Pat. No. 5,947,681, entitledPRESSURE BALANCED DUAL AXLE VARIABLE NOZZLE TURBOCHARGER provides aplurality of individual blades placed in the intake nozzle of theturbine, which can turn in order to reduce or increase the area of thenozzle and the flow volume. The piston type, which is exemplified inU.S. Pat. Nos. 5,214,920 and 5,231,831 both entitled TURBOCHARGERAPPARATUS, and U.S. Pat. No. 5,441,383 entitled VARIABLE EXHAUST DRIVENTURBOCHARGERS uses a piston or a cylindrical wall which can be displacedconcentric to the axis of rotation of the turbine in order to reduce theintake area of the nozzle. In most cases the variable-geometryturbocharger of the piston type includes blades with a leading edgewhich is fixed with respect to the flow of air, which are either mountedon the piston or on a stationary nozzle wall facing the piston and whichenter into slots in the opposite surface during displacement of thepiston.

In variable-geometry, piston-type turbochargers of the prior art thechallenge has been to maximise the aerodynamic performance balanced bythe tolerancing of the contact surfaces, principally of the blades andthe reception slots which are subjected to an extreme temperaturevariation and to mechanical stress, as well as to provide a means foractuating the piston according to a configuration which can be easilymanufactured.

SUMMARY OF THE INVENTION

A turbocharger incorporating the present invention has a casing having aturbine housing receiving exhaust gas from an exhaust head of aninternal combustion engine at an intake and having an exhaust outlet, acompressor housing having an air intake and a first volute, and acentral housing between the turbine housing and the compressor housing.A turbine wheel is mounted in the turbine housing to extract the energyfrom the exhaust gas. The turbine wheel is connected to a shaft whichextends from the turbine housing through a shaft bore in the centralhousing and the turbine wheel has a substantially complete rear disc andmultiple vanes. A bearing mounted in the shaft bore of the centralhousing supports the shaft for rotational movement and a vane wheel isconnected to the shaft facing the turbine wheel and enclosed in thecompressor housing.

A substantially cylindrical piston is concentric to the turbine wheeland can be displaced parallel to an axis of rotation of the turbinewheel. A plurality of blades extend substantially parallel to the axisof rotation from a first end of the piston in the proximity of the reardisc. A heat screen is engaged at its external circumference between theturbine housing and the central housing and extends radially inwardstowards the axis of rotation. The rear disc of the turbine wheel isembedded in the heat screen for the smooth flow of exhaust gas in thevanes. The heat screen also has a plurality of slots receiving theblades. An actuating device is provided to displace the piston from afirst position in which the first end is in the proximity of the heatscreen to a second position in which the first end is remote from theheat screen.

BRIEF DESCRIPTION OF THE DRAWINGS

The details and features of the present invention will be betterunderstood in relation to the detailed description and the drawings inwhich:

FIG. 1 is an elevation in transverse cross-section of a turbochargerusing an embodiment of the invention;

FIG. 2 is a top view of a first embodiment of the heat screen;

FIG. 3 is a top view of a second embodiment of the heat screen;

FIG. 4 is an elevation in transverse cross-section of an embodiment ofthe invention with an aerodynamic shield in association with the heatscreen;

FIG. 5 is an exploded view of the actuating device;

FIG. 6 is a detailed view of the quick-connect connection between theswivel pipe connector and the diaphragm assembly.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings FIG. 1 shows an embodiment of the invention for aturbocharger 10 which includes a turbine housing 12, a central housing14 and a compressor housing 16. A turbine wheel 18 is connected by theshaft 20 to an impeller 22. The turbine wheel converts the energy of theexhaust gas of an internal combustion engine provided with an exhausthead (not shown) with a volute 24 in the turbine housing. The exhaustgas is expanded through the turbine and exits from the turbine housingvia the outlet 26.

The compressor housing includes an intake 28 and an outlet volute 30. Arear plate 32 is connected by bolts 34 to the compressor housing. Therear plate is, in turn, fixed to the central housing by means of bolts(not shown). A first annular seal 36 is engaged between the rear plateand the compressor housing and a second annular seal 38 is engagedbetween the rear plate and the central housing. Bolts 40 and fixingwashers 42 connect the turbine housing to the central housing.

Journal bearings 50 mounted in the shaft bore 52 of the central housingsupport the shaft during rotation. A clamping collar 54 mounted on theshaft adjacent to the impeller engages an abutment bearing 56 forcedbetween the central housing and the rear plate in the illustratedembodiment. A sleeve 58 is engaged between the clamping collar and theimpeller. A rotational seal 60. such as a piston segment, provides aseal between the sleeve and the rear plate. A circlip 62 urges thejournal bearing into the bore and a nut 64 urges the impeller and thebearing components onto the shaft.

The variable-geometry mechanism of the present invention includes asubstantially cylindrical piston 70 moving into the turbine housingwhich is concentrically aligned on the rotational axis of the turbine.The piston can be displaced longitudinally by means of a cross-piece 72,having three branches in the illustrated embodiment, being attached tothe piston and being attached to an actuating shaft 74. The actuatingshaft enters a bushing 76 extending through the turbine housing and isconnected to an actuating device 77. In the illustrated embodiment theactuating device is mounted on projections on the turbine housing usinga support 78 and bolts 80.

The piston slides in the turbine housing by means of a low-frictionattached piece 82. A cylindrical seal 84 is inserted between the pistonand the attached piece. The piston can be displaced from a closedposition illustrated in FIG. 1, substantially reducing the area of theintake nozzle which extends from the volute 24 to the turbine. In thefully open position, a radial projection 86 on the piston enters arecess 88 which defines the course of the piston.

The blades 90 of the nozzle extend from the radial projection on thepiston. When the piston is in the closed position the blades are housedin a recessed portion of the moulded piece of the central housing. Aheat screen 92 is engaged between the turbine housing and the centralhousing. The screen is of a suitable shape to extend into the cavity ofthe turbine housing from the interface between the central housing andthe turbine housing and to provide a wall inside the intake nozzle ofthe turbine. The turbine wheel includes a substantially complete reardisc and a central orifice 94 (best seen in FIGS. 2 and 3 as describedhereinunder) in the screen receives the rear disc of the turbine wheelin an embedded manner in order to provide a substantially smoothaerodynamic trajectory from the outlet of the volute of the turbinehousing to the turbine wheel.

FIG. 2 shows a first embodiment of the heat screen including closedslots 96 to receive the blades 90. The circumference of the orifice 94,in which the rear disc of the turbine wheel is embedded, is inside theportion of the profiles of the slots housing the rear edge of theblades. This embodiment provides an optimal aerodynamic profile but theproduction constraints and the tolerances between the slots and theblades may prevent effective use of this embodiment in someapplications.

FIG. 3 shows a second embodiment of the heat screen which provides anopen profile at the rear edge of the slots, adjacent to the centralorifice in order to reduce, to some extent, the tolerance requirementsof these slots. The profile of the slots extends along and beyond theexternal surface of the vanes substantially as far as the diameter ofthe rear disc of the turbine wheel but the profile along the internalsurface of the blade ends by leaving an orifice, generally designated98, joining the slot to the central orifice. In both embodiments, thefact of embedding the eccentricity of the hub of the turbine wheel andthe rear disc in the central orifice minimises the clearance and theblade-free space between the rear edges of the blades and the diameterof the peak of the turbine blades of the turbine wheel.

FIG. 4 shows an aerodynamic shield 100 engaged between the heat screenand the central housing. The shield prevents the recirculation ofexhaust gas leaks from the cavity of the rear disc of the turbine wheelinto the recess in the central housing which houses the blades when thepiston is in the closed position. Preventing the recirculation from thecavity of the rear disc encourages a smooth flow from the intake nozzleinto the vanes of the turbine wheel. In the illustrated embodiment theshield is fixed between the heat screen and the central housing by theaction of a spring comparable to a domed elastic washer.

The system for actuation of the piston in the embodiment illustrated inthe drawings is a pneumatic actuating device 77 having a casing base 102fixed to a support 78 as illustrated in FIG. 1. As shown in FIG. 1 andin more detail in the exploded view of FIG. 5 a diaphragm 104 is engagedbetween the casing base and a cover 106. A spring plate 108 incombination with the cover urges a spring 110 for the purpose ofrestoring the force on the diaphragm. The cover is held in position byan actuating device cap 112 which contains a vacuum intake 114 foractuation purposes. A seal 116 is provided between the cap and thecover.

An actuating hub 118 is fixed to the diaphragm by an elastic washer 120which also acts as a plate for the spring 110. The actuating hub isconnected to the shaft by a quick-connect connection 122 which will bedescribed in more detail hereinunder. A small-diameter centringconnection 124 on the shaft enters a counter bore 126 in the hub.

As shown in FIG. 1 the linear displacement of the shaft is utilised bydiametral extensions 130 on the shaft which slidingly enter a bore 132in the turbine housing. In some embodiments a deflector 134 is mountedaround the shaft in order to divert leaks of gas via the bushing 76 andget them away from the actuating device.

The quick-connect connection illustrated in detail in FIGS. 5 and 6 ismade of sheet metal shaped in to a substantially cylindrical shape witha longitudinal slot 140. Oppositely positioned cut-outs 142 in the wallof the cylinder provide clearance for tongues 144 which are lowered intothe cylinder. A first set of tongues is adapted to engage in a slot 146in the shaft while a second set of tongues is adapted to engage in aslot 148 in the actuating hub. The elasticity of the sheet metal tonguesand of the slotted cylinder permits insertion of the shaft and of thehub into the quick-connect connection by the instant engagement of thetongues in the slots, thus overcoming the need for any threadedconnection between the shaft and the hub. The alignment connection andthe core in the hub maintain the axial alignment of the assembly.

An additional advantage of the quick-connect configuration is thepossibility of removing the actuating device from the turbochargerwithout significant disassembly and—even more importantly—in mostmounting configurations, without removing the turbocharger from thevehicle. The support 78 is loosened from the turbine housing and acompression tool is used to remove the tongues from the slots and topermit the shaft and/or the hub to be withdrawn from the quick-connectconnection.

An alternative embodiment for the quick-connect connection is astar-shaped spring washer which is wedged in a cut-out in the actuatinghub. By inserting the shaft into the hub, the star-shaped spring washerengages a shoulder on the shaft. A circumferential edge of the cut-outis crimped to fix the star-shaped spring washer in the cut-out. Thesecond embodiment allows for reduced length over the overall coupling.

Having described the invention in detail as required by the law ofindustrial property, those skilled in the art will see modifications andsubstitutions which can be made to the specific embodiments disclosedherein. Such modifications and substitutions are within the scope andintention of the present invention as defined in the following claims.

What is claimed is:
 1. A turbocharger (10) comprising: a casing having aturbine housing (12) receiving exhaust gas from an exhaust head of aninternal combustion engine at an intake and having an exhaust outlet, acompressor housing (16) having an air intake and a first volute, and acentral housing (14) between the turbine housing (12) and the compressorhousing (16); a turbine wheel (18) mounted in the turbine housing (12)and extracting the energy from the exhaust gas, the said turbine wheel(18) connected to a shaft (20) extending from the turbine housing (12)through a shaft bore (52) in the central housing (14) and the saidturbine wheel (18) having a rear disc and multiple vanes; a bearing (50)mounted in the shaft bore (52) of the central housing (14), the saidbearing supporting the shaft (20) for rotational movement; a vane wheel(22) connected to the said shaft (20) facing the turbine wheel (18) andenclosed in the compressor housing (16); a substantially cylindricalpiston (70), concentric to the turbine wheel (18) and able to bedisplaced parallel to an axis of rotation of the turbine wheel (18); aplurality of blades (90) extending substantially parallel to the axis ofrotation from a first end of the piston in the proximity of the reardisc; a heat screen (92) engaged at its external circumference betweenthe turbine housing (12) and the central housing (14) and extendingradially inwards towards the axis of rotation, the rear disc of theturbine wheel housed in the heat screen (92) for the smooth flow of theexhaust gas in the vanes, the said heat screen (92) also having aplurality of slots (96) receiving the blades (90); and means (77) fordisplacing the piston (70) from a first position in which the first endis in the proximity of the heat screen to a second position in which thefirst end is remote from the heat screen, further characterised by: anaerodynamic shield (100) located between the rear disc of the turbinewheel (18) and the central housing (14) and having an externalcircumferential portion engaging an internal circumferential portion ofthe heat screen (100), the said aerodynamic shield having an internalcircumferential portion engaging the central housing (14) in theproximity of the shaft bore.
 2. Turbocharger as defined in claim 1,wherein the heat screen (92) has a central orifice in which the reardisc is embedded and wherein the plurality of slots in the heat screen(92) each have a closed rear edge in the proximity of the centralorifice.
 3. Turbocharger as defined in claim 1, wherein the heat screen(92) has a central orifice in which the rear disc is embedded andwherein the plurality of slots of the heat screen (92) each have aprofile extending beyond an external surface of the associated bladesubstantially as far as the diameter of the central orifice, the saidprofile extending along an internal surface of the associated bladeending at the central orifice leaving an orifice at the rear edgeconnecting to the central orifice.
 4. Turbocharger as defined in claim1, wherein the means for displacing the piston comprise; a cross-piece(72) having a plurality of branches attached to the piston, the saidbranches converging towards an actuating shaft concentric to the axis ofrotation; an actuating device (77) having an actuating hub (118); and aquick-connect connection means (122) to connect the actuating shaft andthe actuating hub.
 5. Turbocharger as defined in claim 4, wherein theactuating device is a pneumatic actuating device having a diaphragmconnected to the actuating hub (118).
 6. Turbocharger as defined inclaim 4, wherein the quick-connect connection means has a cylinder madeof sheet metal having a longitudinal slot (140) and at least one pair ofelastic tongues (144) spaced apart in an opposite longitudinalorientation along the cylinder and extending into it, one of the pair oftongues being adapted to engage a circumferential slot (146) in theactuating shaft and the second of the pair of tongues being adapted toengage a circumferential slot (148) in the actuating hub (118). 7.Turbocharger as defined in claim 6, wherein the actuating hub (118)includes a counter bore (126) adapted to receive, in a close-fittingmanner, an alignment connection (124) extending from the actuatingshaft.